In a cellular communications system, subscribers or users may want to transfer digital information over the air using their subscriber unit. To facilitate this wireless transfer of digital information, many subscriber units offer optional connections for receiving digital information from a computer, a facsimile machine, or other data source.
The advance of digital cellular communications systems allows new possibilities for data transmissions. Instead of converting digital bits (pulses) into audio signals that are sent on the radio channel, the digital bits are sent directly into the phase modulator of the digital transmitter in the subscriber unit. This approach allows much higher data transmission rates. When the digital bits are received in the cellular infrastructure, they must be converted to a format that can be transmitted through the public switched telephone network.
With reference now to the data flow diagram in FIG. 1, call setup procedures for code division multiple access (CDMA) circuit data and fax services involves several data and command transfers between a subscriber unit, a radio subsystem, and an interworking unit that contains one or more modems. The subscriber unit is the unit on the user's side of the radio frequency interface. The radio subsystem and the interworking unit are each a part of what may be referred to as cellular infrastructure, which is on the other side of the radio frequency interface. The cellular infrastructure may be defined as the equipment and software that couples the subscriber to the public switched telephone network. As shown in FIG. 1, the subscriber unit sends a request for a data connection 10 to the radio subsystem, or base station. The radio subsystem then requests a data circuit 12 in the interworking unit. This request may be implemented in a CDMA system by using ANSI T1.617 protocol. The interworking unit responds with an ANSI (American National Standards Institute) T1.617 connection acknowledgment response 14. ANSI T1.617 is a call processing protocol to setup and tear down a data circuit between the radio subsystem and the interworking unit in a cellular communication system.
Next, the subscriber unit and the interworking unit exchange commands and data to setup a data communication protocol stack 16, such as an IS-99 stack in a CDMA system. After the data protocol stack is setup, the subscriber unit and the interworking unit exchange AT commands and responses 18 in order to configure the modem according to the user's need. As shown in FIG. 1, several commands and responses 18 may be necessary to properly configure the modem and the data connection. Such AT commands may include commands to instruct the modem to communicate at a specified baud rate, to change the carrier detect timeout, or to perform any other similar command from the extensive list of AT commands.
After the modem is configured, the interworking unit requests a PSTN data circuit 20. This step may be accomplished by using ANSI T1.607 protocol in a CDMA communications system.
To indicate that the PSTN connection 22 has been established, the radio subsystem sends the interworking unit a connection acknowledgment signal 24, which in a CDMA system uses ANSI T1.607. Thereafter, the radio subsystem performs modem negotiation 26, which is a process that prepares the modems to communicate with each other.
After modem negotiation 26, the modem in the interworking unit responds to the subscriber unit with a connect indication. Thereafter, data transfer 30 between the subscriber unit and the modem may proceed.
As shown in FIG. 1, the prior art method of initiating a data transfer requires that AT commands 18 or other similar configuration commands be sent from the subscriber unit to the modem in the interworking unit. These commands are sent over the air interface and use billable air time during the transfer. Such billable air time increases the cost of data transfer from a subscriber unit to a data receiver. Furthermore, while the subscriber laboriously enters commands to configure the data connection, other users may be blocked from access to the cellular system. Such blocking may be reduced if time required to setup the data connection is reduced.
Therefore, a need exists for an improved method and system for initiating a data transfer wherein the air time required to configure the data connection is reduced or eliminated.